There is a need for apparatus to reliably detect nuclear detonations occurring within a range that will cause danger from "fallout" radioactive particles. For example, if a nuclear detonation occurs at a distance of approximately 10 to 100 miles, there may not be great danger from direct blast radiation, but the radioactive fallout particles will, usually in a matter of minutes or hours, be a serious threat to life and also to food and certain equipment such as radio, radar, power stations, military equipment, medical supplies, etc. Suitable detection or sensor apparatus will sound an alarm so that suitable and timely precautions can be taken to safeguard the lives of humans and animals (by the use of fallout shelters, for example) and to protect food, equipment, etc. A complete nuclear detonation sensor system may comprise a radiation sensor (for electromagnetic radiation, optical radiation, or both) and a seismic sensor for detecting the subsequent earth tremor.
It is important that the sensor system be reliable, both as to indicating all nuclear detonations within its range, and also as to not causing false indications. False indications may cause unnecessary expenses and perhaps public panic, and also will adversely affect credibility of the alarm system so as to impair its effectiveness in the event of a valid indication of nuclear detonation.
The electromagnetic sensors in such systems have been prone to be responsive to electromagnetic energy associated with lightning, thus giving false indications of nuclear detonations. This problem has not been readily solved, because of the similarity of electromagnetic waveshapes produced from nuclear detonations and from lightning strokes.